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1117 Lone Palm Avenue, Suite B <br /> � Q Modesto, CA 95351 <br /> r, <br /> vaww.akc-envi[o.com <br /> 209.579.2221,. f. <br /> Fax 209.579.2225. <br /> ' <br /> �AS �10C A T E3 I N C <br /> y <br /> '- January 24, 2003 D <br /> 54.22493.0001 HIECEHE <br /> Ms. Margaret Lagorio JAN 2 8 2003 <br /> San Joaquin County Environmental Health Department ENVIRONMENT HEALTH <br /> 304 East Weber Street, Third Floor PERMIT/SERVICES <br /> Stockton, California 95202-2708 <br /> Subject: Monitoring Report Fourth Quarter 2002, Eggiman Property, 1112 East Harding <br /> Way, Stockton, California <br /> Dear Ms. Lagorio: <br /> This report presents the results of quarterly groundwater monitoring and sampling performed on <br /> October 14, 2002 by ATC Associates Inc. at the site located at 1112 East Harding Way, <br /> Stockton, California (Figure 1). Monitoring was performed to determine groundwater flow <br /> direction and the hydraulic gradient in the uppermost aquifer. Sampling was performed to <br /> monitor the petroleum hydrocarbons in the groundwater at the site. <br /> BACKGROUND <br /> In April 1987, SEMCO removed and disposed of two 1,000-gallon regular gasoline underground <br /> storage tanks (USTs), associated piping, and fuel dispenser from the locations shown on Figure <br /> 2. A soil sample was collected from the end of each tank at approximately 17 feet below ground <br /> surface. Analytical testing indicated the collected samples contained detectable concentrations <br /> of petroleum hydrocarbon constituents. The excavation was subsequently backfilled to the <br /> ground surface. <br /> On July 24, 1997, to investigate the extent of residual soil contamination at the site, a total of six <br /> soil borings were advanced to depths ranging from approximately 16 to 31 feet below ground <br /> surface (bgs). Detectable concentrations of total petroleum hydrocarbons as gasoline (TPHg), <br /> total petroleum hydrocarbons as diesel (TPHd), and benzene, toluene, ethylbenzene, and xylenes <br /> (BTEX) were observed in soil samples collected from the site. The distribution of petroleum <br /> constituents beneath the site has been essentially defined and appears to be limited laterally to <br /> the immediate vicinity of the former tank pit. The highest concentrations were reported between <br /> 10 and 20 feet bgs and generally attenuate rapidly with depth. Only low concentrations of <br /> toluene (0.064 mg/kg) and xylenes (0.012 mg/kg) were detected at approximately 30 feet bgs in <br /> one boring, the maximum depth explored. Attempts were made to further advance the Geoprobe <br /> unit in several of the borings, however probe refusal was encountered at depths ranging from' <br /> approximately 16 to 30 feet bgs due to the hardness of the formation. The results of the <br /> subsurface investigation were summarized in Smith Technology's Summary Report, Subsurface <br /> !. Investigation, dated December 22, 1997. <br /> w:lwordpro1224931Reponft"II WENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />